Novel method of producing ion exchange membrane

Abstract

A method of producing an ion exchange membrane comprising irradiating a polyethylene film not more than 150 mu m thick with ionizing radiation for a total dose of 1-30 Mrads in vacuum or in an inert gas, bringing the irradiated film into contact with a 15 to 50 wt % aqueous solution of acrylic acid and/or methacrylic acid at 15 DEG to 50 DEG C. to have acrylic acid and/or methacrylic acid graft copolymerized onto polyethylene, followed by treatment of the graft copolymer with a 2 to 10 wt % aqueous solution of potassium hydroxide.

What is claimed is: 
     
       1. A method of producing an ion exchange membrane having an electrical resistance of 50Ω cm or lower and a uniform graft distribution comprising irradiating a polyethylene film not more than 150 μm thick with ionizing radiation for a total dose of 1-30 Mrads in vacuum or in an inert gas,   then contacting the irradiated film with a 15 to 50 wt% aqueous solution of acrylic acid and/or methacrylic acid, substantially free of oxygen and which contains a homopolymerization inhibitor of a ferrous salt or a cupric salt to graft acrylic acid and/or methacrylic acid onto the polyethylene film, for a time sufficient to provide a degree of grafting of at least 60%, and   then treating the grafted film with a 2 to 10 wt% aqueous solution of potassium hydroxide at a temperature of room temperature to 90° C. for 5-120 minutes.   
     
     
       2. The method as defined in claim 1 wherein said irradiation is carried out in a nitrogen atmosphere. 
     
     
       3. The method as defined in claim 1 wherein said inhibitor is added in an amount within the range of from 0.01 to 25% by weight based on the amount of the aqueous solution of monomer. 
     
     
       4. A product of high chemical stability and mechanical strength obtained by the method of claim 1 having a thickness not more than 150 μm, a degree of grafting of at least 60% with a uniform graft distribution throughout its thickness, and an electrical resistance not greater than 50 ohms cm. 
     
     
       5. A method as defined in claim 1 wherein said aqueous solution is made substantially free of oxygen by freeze-degassing the aqueous monomer solution in vacuum or by displacing oxygen with nitrogen or other inert gas by bubbling said nitrogen or other inert gas through the solution.